Metallurgical tuyeres are utilized in pyro-metallurgical processes for injecting a gas, such as air, below the surface of a molten metal bath. The molten bath may be ferrous, such as in steel making processes, or non-ferrous, such as in copper converting processes.
A major problem which has plagued the metallurgical industry for years, has been the erosion/corrosion and general deterioration of the tuyere pipes and surrounding refractory which is experienced within a molten bath during the blowing process. The chemical energy generated at the tuyere tip appears to create a thermal and chemical environment which results in a situation wherein the tuyere rate of wear is markedly greater than the refractory brick rate of wear. Such situation results in a mechanism of failure that is mechanically related, rather than corrosion/erosion related, as previously envisioned in the art.
As pointed out in U.S. Pat. No. 3,627,510, during a copper converting operation, molten copper has a tendency to freeze to a greater or less extent over the end of and up into the tuyeres, thereby reducing the cross-sectional area of the tuyeres and the gas flow through the tuyere pipes. Such build-up or accretion of solidified copper matte is also known as a "knurdle." The formation of a knurdle on the tuyere nozzle and the effects thereof on the surrounding refractory brick upon its removal, has been considered to be undesirable in the industry.
Various attempts have been made in the past to eliminate the formation and effects of knurdles, including the use of water-cooled tuyeres, such as shown in U.S. Pat. Nos. 746,238 and 870,925, and Japanese Patent Application No. 48-27166. Generally, the tuyere pipe has either been formed of cast iron or plain carbon steel, as set forth in U.S. Pat. No. 942,346, or stainless steel, as set forth in U.S. Pat. No. 3,627,510, although the U.S. Pat. No. 870,925 suggested the use of a seamless brass tuyere pipe. Due to the relatively low thermal conductivity and heat diffusivity of such materials, the cooling of base portions of such tuyere pipes did not function to maintain a controlled temperature at the tip of the nozzle communicating with the molten bath. Further, when water cooling was attempted along the longitudinal extent of the nozzle, the tuyere pipe was protected only until such time as the surrounding refractory deteriorated, which then permitted the ultimate consumption of the tuyere pipe per se, and the catastropic release of water into the molten metal bath.
In addition, the use of water cooled copper tuyeres and water cooled furnace cooling plates made of copper were known in the art as shown by United Kingdom Pat. Nos. 1,072,121 and 2,047,860 A and U.S. Pat. No. 3,598,382. Here again, however, the required cooling was provided by means of water which circulated the full longitudinal extent of the tuyeres and cooling plates, which as previously mentioned, produces a safety hazard due to the deleterious effects produced upon water leakage. Canadian Pat. No. 1,006,695 relates to cooling devices for protecting refractory linings of furnaces wherein solid probes are positioned within the refractory and are water cooled externally thereof. However, the Canadian patent is not concerned with the deleterious effects products at the end of a hollow tuyere pipe during the blowing of gas or oxygen enriched air into a molten metal bath. In basic oxygen steel making, oxygen lances, formed of wrought tubular sections, are provided with water-cooled silver copper casings to dissipate the heat generated during the blowing of the surface of the melt, as disclosed on page 49 of the July, 1970, issue of Materials Engineering.
As shown in U.S. Pat. No. 3,395,910, refractory sheaths consisting of refractory cement or blocks have been utilized to protect the tuyere pipes from the molten metal in which they are submerged, whereas U.S. Pat. No. 3,627,510 suggests that the tuyere pipe may be coated with a refractory material to insure a good fit and prevent fusion of the pipes during service.
The present invention overcomes the problems of knurdle size control, tuyere pipe burn-back, and adjacent refractory deterioration, by utilizing external fluid cooling in conjunction with proper thermal conductivity and heat diffusivity design within a tuyere pipe. A range of control of heat extraction is provided so as to match the process temperature variability of the molten bath adjacent to the tuyere nozzle.